Transmission



Oct. 19, 1954 F, R. MGFARLAND 2,691,940

TRANSMISSION Filed July 28 1950 3 Sheets-Sheet 2 FOREST R., c FAR/.AND

' MMLMMQmfm Oct. 19, 1954 ER. MOFARLAND 2,691,940

FOREST R. Mc FARLAND Patented Oct. 19, 1954 UNITED STATES PATENT yOFFICE TRANSMISSION Forest R. McFarland, Huntington Woods, Mich.,

assignor to Packard Motor Car Company, Detroit, Mich., a corporation of Michigan Application July 28, 1950, Serial No. 176,391

(Cl. S-4) 14 Claims. l

This invention relates to a control for a hydraulically operated device, such as a variable speed power transmission for automotive vehicles. Such devices usually employ two pumps for supplying the uid pressure needed to operate the transmission; one pump is connected to the engine at all times to supply fluid under pressure for starting the vehicle in motion, and the other pump is connected at all times to some member rotatable with the rear wheels, so as to supply iluid under pressure when the vehicle is moving. Since pump pressure .will vary as a function of speed, the variation in pressure produced by the pump rotatable with the rear wheels is utilized to control changes in speed ratio or some other operation of the transmission. Each pump has to be of suiiiclent size and capacity to carry the load individually. When the vehicle is in motion, however, both pumps normally operate and since one is suicient to carry the load, it is desirable to remove the other from the line, thereby economizing on the power required to operate the transmission.

One such transmission utilizing hydraulically operated clutches and brakes to effect speed ratio changes is disclosed in my co-pending application, Serial No. 71,128, led January 15, 1949.

The transmission disclosed in the aforesaid copending application includes, in addition to hydraulically operated brakes and clutches, a hydrodynamic torque converter which for optimum efficiency must be filled with fluid under pressure while it is in operation. The pressure of the fluid in the converter is lower than the pressure required to operate the various clutches and brakes. Furthermore, in view of the different torque reactions handled by the brakes, different operating pressures must be available, for the brakes.`

The principal object of this invention is to provide a hydraulic control system for a variable speed power transmitting device for an engine wherein the device is equipped with two pumps, the control system being adapted to select one of the pumps automatically under certain conditions for supplying uid under pressure to the system, the other pump being operated at a reduced pressure at the time, so as to reduce the load on the engine.

A more specific object of this invention is to provide a pump selecto!` valve for a hydraulic control system utilizing two pumps, said valve being adapted to assume a plurality of positions in accordance with the pressure developed by one of the pumps, the pressure. in turn, being a funcf tion of the speed at which the selected pump is driven.

A still more specific object of this invention is to provide a pump selector valve for a hydraulically operated device, utilizing two pumps, wherein means are provided for selecting one pump while reducing the output pressure of the other pump and then causing the valve to produce two different pressures consecutively from the operative pump; that is, the valve will produce a relatively low pressure until the operative pump reaches a predetermined speed of rotation at which point the pressure will be increased materially.

Another specific object of this invention is 'to provide a control system for a hydraulically operated power transmitting device, the latter having two pumps as a source of operating pressure, wherein a pump selector valve is utilized along with a check valve which blocks the output of one pump while the other is operating and with a vent Valve for one pump, the valve being in part hydraulically balanced, the hydraulic balance, in turn, being controlled by the selector valve.

These and other objects of this invention will become apparent from the following detailed description when taken together with the accompanying drawings in which Fig. 1 is a schematic diagram of the hydraulic control system of a power transmission of the type shown in the aforesaid co-pending application, Serial No. 71,128, filed January 15, r1949. Said schematic diagram showing the novel pump selector valve and associated check valve and vent valve;

Fig. 2 is a schematic diagram of the hydraulic system and selector valve shown in Fig. 1, the valve and system being shown in the positions they assume when the valve has rendered one pump inoperative to supply fluid under pressure and has rendered the second pump eiective; and,

Figs. 3 to 5, inclusive, are sections taken through just the pump selector valve of Figs. 1 and 2, showing the valve in various stages of operation.

Before describing in detail the arrangement and operation of the parts of the system shown in the drawings, I wish it understood that the disclosure is merely illustrative of a preferred embodiment of this invention and that the invention may be applied to devices other than the transmission disclosed in the aforesaid co-pending application, Serial No. 71,128, filed January 15, 1949.

Referring now to the drawings for a detailed description of the invention and particularly toV Fig. 1, there is shown schematically a hydraulic., torque converter I0 comprised of a rotating con-4 a tainer I I to which are secured pump impeller blades I2 and within which are disposed a two stage turbine element I3 and a vaned reaction element I4, said two stage turbine element and vaned reaction element being sealed with the respect to container II to form a rotatable toroidal container. As shown in my co-pending application, Serial No. 71,126, housing Ii is connected to the engine so as to be rotatable therewith, while turbine element I3 is splined to an intermediate shaft which may be connected either directly or through gearing to a transmission output shaft from which the wheels of the vehicle are driven.

A pump I5, shown schematically as a rectangle, is driven directly from housing II and thus lis driven whenever the engine is operating. lSaid pump I5 is preferably of the gear type, but any pump adapted to provide a positive displacement and hence a determinable fluid pressure may be used. A second pump I6 is driven from the output shaft of the transmission and is likewise preferably of the gear type. Pump I6 has materially less capacity than pump I5. Fluid for the system is obtained through a con duit I1 from a central reservoir or sump and is fed through one branch I8 to pump I5 and through another branch I9 to pump I8. In branch I8 is disposed a pressure regulating valve 26 which is comprised of a plunger 21 having two lands, 2I and 22, connected by a stem 23 to form a peripheral groove 23. Land 22 has a small bleed opening 24 connecting both sides of the land. A spring 25 normally holds plunger 21 in the position shown in Fig. 1. In this position, land 2l bridges a groove 26 in bore 28, said groove 26 being connected to a passageway 29 which constitutes the inlet for pump I5. The outlet for pump I5 is shown at 30v and is alway aligned with the peripheral groove around the plunger which, in turn, is always aligned with a passageway 3l leading to a check valve 32.

Pump I6 is connected directly to branch I9 at all times, so that iluid from the sump is always available to said pump I6. The pump outlet is connected through a passageway 33 to the same. check valve 32.

Check valve 32 is comprised of a valve body 34 having a bore 35 therein in which is slidable a valve plunger 36. Said plunger is comprised of two lands, 31 and 38, connected by a stem 39 which, with lands 3T and 38, forms a peripheral groove in plunger 36. A short stem 46 extends to the leftv ofv land 31, as viewed in Fig. 1 and is of a length to cause land 31 to close a port 4I in body 34 when said stem 46 abuts on the end wall 42 of valve body 34. Passageway 3l terminates vin a port 43r which is located to the left of port 4I, as viewed in Fig. 1, and is so spaced from end wall 42 that when stem 46 abuts on end wall 42, port 43 is not covered by land 31. This means that the left hand end of plunger 36, as viewed in Fig. 1 is always exposed to the pressure of the fluid in passageway 3|.

Passageway 33 from pump I6 terminates in a port 44V in the right hand end wall, as shown in Fig. 1, of the valve body 34 and thus. the right hand end of plunger 36, as viewed in Fig. 1, is always exposed to the pressure of the uid in conduit 33.

It is apparent from the description of the valve plunger 36 and its associated passageways and ports that when the pressure in passageway 3l exceedsthe pressure in passageway 33., plunger 4 36 will move to the right to the position shown in Fig. 1, and when the pressure in passageway 33 exceeds that in passageway 3|, plunger 36 will move to the left until stem 40 strikes end wall 42.

A port in valve block 34 is located near the right hand end of the block-,gas viewedin Fig. 2, such that land 38 .covers 'po'r't 45 insfcne. ,extreme position of the plunger 36 and in the other extreme position uncovers port 45 to allow iluid from port 44 to pass out of the block. Port 45 is connected through a short passageway 46 to a pressure line 41, and port 4I is connected to a short passageway ,48 to the same pressure line 41. Thus, check valve 36 is effective in one position to admit fluid under pressure from pump I=5 to pressure line 41 while closing off the line leading to pump I6, and in its other position, closes oil port 4I which, in turn, closes off the outlet of pump I5 and at the same timer connects pump I6 to pressure line 41. lThis, operation is automatic and is determined solely by the rela# tive pressures produced by the two pumps "I5 andk I6 and transmitted to opposite sides 'of plunger 36. It is also a'means for preventing theout'- put of one pump from draining to the sump through the other pump.

Pressure line 41 is connected to al portv 49 in a valve block 5U containing the pump selector valve for the system.` Said vvalve is coi'nprisedv of a plunger 5I, havinga recess 52 at one end in which is received a closed-endtube 53. Said tube. is slidable in a'short closed-end 'tube 54 which abuts on the jend o f the hereje in which plunger 5I is slidable.` A. springt? is compressed between the closed end oitube'54v and the closed end of tube 53 soas 'toitend to separate the two. Thel net effect of this` spring pressure is to urge plunger 5I l'to theleit at all times.

Surrounding tube 53 'is a secondspring A58r which is compressed between 4the `open end of tube 54 and the end 59 of a sleeve 66 which is" slidable on the tube 53.' vSaidsleeve B0 is of reduced diameter with respect to the end 59 so as to be slidable within a snap ring6l retained in a groove 62 in valve block 50. v'Snap'ring 6IV limits the movement of sleeve 66 tothe left as viewed in Fig. v1 which,.in turn,`limits the; expanded height of spring 58. I Itis contemplated that spring 58 will be under compression when sleeve 6.0 rests against snap ring V6I.' The ope posite end 63 of sleeve 66 is in the path of 'move-f ment of the end L64 of plungerl 5I 'so' that fas' plunger5lv is movedtothe right,as viewedin Fig. 1, it will strike the end 63fof sleeve 66 and will thereafter move against Athe resistance of spring 58, as transmitted toit by sleeve66. Thus, plunger 5I, in order to move tov the lright as viewed in Fig. 1, must rst compress spring 51` until the plungerend'64 strikes Aend 63 ofsleeve 66, and thereafter the'plunger'4 5Iy must lmove against the combined resistance of springs 51 and 58.

Aligned with port 49' is a relatively wide peripheral groove 65 on plunger 5I which is connected by cross bores 66 inthe plunger 5I tovv a central opening 61 leading to the left hand end 68 of plunger 5I as viewed in- Fig.' 1. Any fluid pressure existing` in port 49 will also be present at the end 68 of. plunger 5I and will tend to move plunger 5I` to the right against` Ethe resistance of spring 51. Should thepressure vin port* 49 become great enough, plungerv 5`I"wil1"move"un til it strikes sleeve 66, vand then will be held there Auntil theY pressure in port 49 increases to the value required to overcome both springs 51 and 58.

To one sideY of port 49 in block 50 is another port 69 which is connected through a conduit 19 and a port II located on the spring side of land 2I to bore 28 in valve 20. Fluid under pressure is conducted from port 49 through peripheral groove 65 to port 69 and thence through conduit 10 and port 'H to the spring side of land 2l, thereby adding fluid pressure to the pressure of spring 25 to urge the plunger 21 toward .the position shown in Fig. 1. The pressure of spring 25 and the fluid pressure will be opposed by pump pressure, acting upon the side of land 22 opposite stem 23, the fluid passing to said side through bleed opening 24. This pump pressure is initially established by the spring and is then increased by the pressure ow in line 1I from the selector valve 5 I. As will be shown later, the fluid pressure acting with spring 25 will vary and gradually decreaseuntil it becomes substantially zero. When the fluid pressure disappears, all that opposes the outlet pressure of pump I5 is spring 25, and hence valve 21 will rise and uncover port 29 to dump the fluid back into the intake side of the pump until the fluid pressure is reduced to the spring pressure at which it will be stabilized.

Adjacent port 49 in block 58 is a relatively wide port 12 which is connected by means of a conduit 13 tothe sump. Between ports 49 and 'I2 is a port 14 which is connected by means of a conduit 15 to the interior to torque converter I9. Adjacent port 69 is a port 16 which is connected by suitable means (not shown) to the sump. At the extreme right of value block 50, as viewed in Fig. 1, is a port 11 which is connected by means of a conduit 18 to a servo motor 19 which may be used to operate the reverse brake of the transmission.

The operation of the plunger 5I, pumps I5 and I6 and associated apparatus described above will now be detailed.

The relative positions of the valves when the engine is inoperative and the Vehicle is stationary is shown in Fig. l. Under these conditions, neither pump I5 .nor I6 is operating and, hence, there is no iuid pressure in the system. When the engine is started and the vehicle is standing still with the engine idling, pump I5 is operating and drawsl fluid from the sump through conduits I1 and I 8, groove 26 and conduit 29 and discharges fluid at increased pressure through pump outlet 39 into the valve 28. From valve 20 the iiuid under pressure passes through passageway 3| to check valve 32, and since pump I6 is not operating, a differential pressure will be established on the plunger 36 to move it toward the right, as viewed in Fig. 1, thereby causing land 38 to cover port 45 to prevent the dumping of the fluid through passageway 46, port 45, bore 35, port 44, and conduit 33 to pump I6.

, The iiuid will be conducted from check valve 32 through pressure line 41 and passageway 48 to port 49 in pump selector valve block 5U. Springs 51 and 5S are unopposed at the moment and, hence, plunger 5I will be at its extreme left hand position as viewed in Fig. 1. In this position, peripheral groove 65 will be in communication with port 49 and also with port 69, thereby conductingfiuid'from pump I5 through conduit 10 and port 1I to the bore 26 of the front pump pressure regulating valve 29. The uid pressure, thus, will be added to the spring pressure and hence the plunger 21 will remain in the position shown. Simultaneously, with the balancing of fluid pressure in pump pressure regulating valve 20, fluid under pressure will be conducted through cross bores 66 and axial bore 61 to the end V68 of plunger 5I. This causes the fluid pressure to oppose the pressure of spring 51, and when the total fluid pressure exceeds the spring pressure, plunger 5I and the pressure of spring 51 opposing the uidpressure acting against end 68 of plunger 5I. As the engine speed increases, the pressure in the output of pump I5 likewise increases thereby increasing the pressure behind plunger 5I and causing the plunger to continue in its movement to the right as viewed in Figs. 1 and 3.

The next position assumed by the valve is shown in Fig. 4. In this position the edge of peripheral groove 65 has completely passed over port 69 so that plunger 5I now covers port 69 and prevents further passage of fluid from port 49 and its connected pump I5 into passage 19 and into the valve bore 28. With the elimination of fluid pressure behind plunger 21, the output pressure of the pump acting through bleed opening 24 to oppose spring 25 then drops to thepressure as established by spring 25. The load on the pump and the power required to drive the pump is thus reduced to a comparatively low value. 'Ihe output pressure of pump I5 will not drop to zero, however, since spring 25 will oppose the pump pressure and will stabilize the pressure at the spring pressure which, of course, is lower than the operating pressure in the system.

At this stage it is assumed that the vehicle is in motion and the pump I6 thereby is in operation. With the reduction of pressure from pump I5, a differential pressure will be established on plunger 32 in the direction of moving the plunger to close port 4I and open port 45. It will be recalled that under these conditions stem 40 abuts on end wall 42 of block 34 so that the position of the-valve is denitely determined with respect to ports 4I and 45. With port 4I closed, pressure from pump I6 may then pass through check valve 32 to conduit 41 and plunger 5I will continue to operate as before.

The condition of the system whenv rear pump I6 takes over is shown in Fig. 2.

Check valve 32 is shown in its left hand position in which port 4I is blocked and port l45 is unblocked. Pump selector valve plunger 5I is shown in Fig. 2 with the edge of a peripheral groove 89 in plunger 5I aligned with the edge of port 69. In the position shown in Fig. 4 the fluid in the bore 23 of pump pressure regulating valve 28 is trapped and remains constant, except for the overflow past land 2i into groove 28. In the position shown in Fig. 2, with the edge of peripheral groove aligned with port 69, the trapped fluid may then escape through conduit 19 and port 69 around peripheral groove 88 to port 16 which, as noted above, is connected to the sump. Thus in the position shown in Fig. 2, the pressure formerly assisting spring 25 is vented and, hence, the pump pressure regulating valve 29 assumes a position shown in Fig. 2; that is, with the output of the pump being fed back to the sump or to the input to the pump so that the load on the pump is reduced to that required to overcome spring 25 only. y

Referring to Fig. 4 again, it will be noted that the end S4. of plunger 5l has been previously coritacted' by the end. (i3` of sleeve 60 which in turn is in Contact with spring 58. At the time of this previous contact the spring loading on plunger 5t was thus brought upto the full pump pressure value is maintained through any further movement to the right of plunger 5l.. Thus, further movement of plunger 5i to the right, as viewed in Fig- 4i, can only take place when the fluid pressure behind end E8 of plunger 5| is sufficiently high to overcome both spring 5l and spring 5B. In terms of pressure, this means. that the pressure in any member connected to plunger 5\l will increase to whatever value springs 5.1 and 58' are set. It is contemplated that pump l5 will be rendered ineective prior to the building up of the pressure. required to overcome springs 5l and 53 and that the. requisite pressure will be supplied by pump t8.

Assuming that pump i6 is in operation and is being driven at a variable speed in accordance with the speed of the vehicle,.its output pressure will likewise vary' and, consequently, may reach a value which may be excessive for the devices controlled by the fluid system. To regulate the output pressure of pump I6, port 'l2y is so located that the edge of peripheral groove 65 will be aligned with the edge of port 12 when the sum of spring. pressures 5l and 58 Will be equal to the maximum pressure desired in the system. This condition is shown in Fig. 5.

It will thus be observed that plunger 5I performs a number of important functions, among which are: (l) l-'iow into converter at reduced pressure due to pump selector valve being under influence of inner spring only at this time, this lowered pressure being for the purpose of securing oil. ow through the converter under limited iront pump capacity under engine idling conditions. (2) Pick up of outer spring and establishing, of proper operating pressure through valve 69 and lead back lines 'HJ and 'IlI to spring side of piston. (3) To relieve pressure behind valve 20 to permit. front pump toV idle when rear pump delivers enough oil to satisfy the system. (4) Blowon means for rear pump when its capacity exceeds demands of system.

`The various hydraulically operated devices of the transmission such as the servomotors for the brakes and clutches are connected to press-ure line 41 through a passageway 8l. and suitable control valves (not shown), and the pressure in passageway 8| may be further modified as desired and as shown in my co-pending application, Serial No. 71,128, led January 15, 1949.

For reverse drive, the reaction produced by the gearing in the aforesaid co-pending application is considerably higher than the reaction for low gear drive and hence the fluid pressure required to apply the brake band is accordingly higher. This increased pressure is obtained by conducting the operating fluid under pressure from servomotor 79 through conduit 'E8 to port ll, the operating fluid being directed to servomotor i9 from passageway Bi through suitable control valvesv as aforesaid. The operating i'luid so conducted will balance out the pressure acting against end 58 of plunger 5| and hence. will result in a higher pressure in the system and particularly in servomotor 19.

, What is claimed is:

1. A control system for a fluid operated variable speed power transmitting `device havinga pump drivenfrom the power input member of the device and a pump driven from the power output member of the device, said system comprising-a check valve, means connecting one side of the check valve to the output of one pump and the other side of said check valve to the output of the other pump, and a pump selector valve connected to the output of the check valve, said pumpv selector valve having a plunger, spring means urging the plunger in one direction, and means for conducting the output of the check valve to the side of the plunger opposite the spring to oppose the action of the spring, said pump selector valve having output ports adapted to be successively connected to or disconnected from the output of the check valve by the plunger, one of said ports being a vent port and serving to limit the maximum pressure produced in the system.

2. A control system as described inclaim I, said system including a pressure regulating valve for the input member driven pump, means to connect said pressure regulating valve tov sai-d vent port of the pumpselector valve when the output member pumpv reaches its normal operating pressure whereby to cause said input member pump to operate at a minimum pressure.

3. A control system as described in claim 1, said system including a pressure regulating valve for the input member driven pump, said pressure regulating valve including a plunger having a peripheral groove aligned at all times with the output of said input member driven pump, one side of the plunger being in hydraulic communication at all times with the groove such that the plunger is urged in one direction by the output pressure of said input member driven pump, said plunger being movable to a position in said one direction wherein the. output of said input'member driven pump is vented, one of the ports in said selector valve connecting the output ci the check valve to the opposite side of. said plunger to balance the. hydraulic pressure on the plunger, and spring means serving to hold the plunger' in its unvented position initially and while they pressure on both sides of the plunger is balanced.

4- A control system as described in claim 1, said plunger spring means of said selector Valve including one spring continuously opposing movement of the plunger over the operating range thereof, and a second spring, saidy second spring being positioned tov be contacted by the plunger ata predetermined position substantially at the end of the range of movement of said plunger and preventing further movement of thev plunger until a substantially greater pressure is produced inthe output of the check valve.

5. A control system for a fluid operated variable speed. power transmitting devi-ce,l a pump in said system driven from the power input member of the device, and a pump in said system driven from the power output member of the device, a pressure regulating valve means in said system, means for connecting said valve means to the output ofv the power input member pump, and means' for connecting the valve means tothe output of the pump driven from the powerl output member', said valve means including; hydraulically actuated means sensitive to pressure supplied by the power output member pump, a vent port in said regulating valve, said hydraulically actuated means uncovering, said port when said pressure reaches a predetermined degree to cause said input member pump to idle when the pump driven 9 from the power output member is supplying fluid at a predetermined pressure.

6. A control system. for a fluidoperated variable speed power transmitting device having -a pump driven from'the powerinput member of the device1 anda pump driven from the power output member of the device, said system comprising a pressure regulating valve having a plunger controlling the output of the power input pump and adapted in one position to vent the said power input pump, fluid means urging the plunger to its venting position, fiuid means opposing the rst" mentioned fluid means, and valve means con trolled by the power output pump for rendering ineffective the opposing fluid means.

7. A control system for a uid operated variable speed power transmitting device having a pump driven from the power input member of the device; said system comprising a pressure regulating valve including a plunges:` controlling the output of the power input pump and adapted in one position to vent the said power input pump, fluid means urging the plunger to its venting position, resilient means opposing the said fluid means such that the fluid pressure produced by the power input pump is limited to a predetermined value, and a pressure regulating and controlling valve connected to the output of the power input pump, said pressure regulating and controlling valve being connected to supply fluid under pressure to the rst pressure regulating valve in opposition to the uid means urging the plunger to its venting position, whereby to enable the said power input pump to suply fluid under high pressure to the system.

8. A control system for a uid operated variable speed power transmitting device having a pump driven from the power input member and a pump driven from the power output member of the device; said system comprising a pressure regulating valve including a plunger controlling the output of the power input pump and adapted in one position to vent the said power input pump, uid means urging the plunger to its venting position, resilient means opposing the said fluid means such that the fluid pressure produced by the power input pump is limited to a predetermined value, a check valve having a plunger, a conduit connecting the output of one pump to one side of the plunger and a conduit connecting the output of the other pump to the other side of the plunger, said plunger being movable in response to differential pressure produced on its sides by the said pumps; outlet ports in said check valve having a common output conduit, one outlet port being connected through the valve to the output of one pump and another outlet port being connected through the valve to the output of the other pump, said check valve plunger in one position closing one outlet port without closing the valve to the output of the associated pump, and a pressure regulating and controlling valve connected to the common output conduit, said last-mentioned pressure regulating and controlling valve being connected to supply uid under pressure to the first pressure regulating valve in opposition to the uid means urging the plunger to its venting position, whereby to enable the said power input pump to continue to supply uid under pressure to the system.

9. A control system as described in claim 8, said last-mentioned pressure regulating and controlling valve being adapted in one position to cut off the supply of fluid under pressure to the first pressure regulating valve infopposition to the uid lil means as aforesaid, whereby fluid pressure in the output of said power input pump drops to its minimum value and said check valve is moved to admit fluid under pressure from the power output pump to the common output conduit.

10. A control system for a fluid operated variable speed power transmitting device having a pump driven from the power input member of the device and a pump driven from the power output member of the device, said system comprising a pressure regulating valve connected to said pumps and having an input port and a'plurality of output ports including a vent port, a plunger in said valve adapted to connect the input port successively to the output ports, said input port being connected to one side of said plunger to urge the plunger in one direction with a force proportional to the fluid pressure in said input port, resilient means opposing the fluid pressure acting on the plunger to establish one range of fluid pressures in the system as the plunger is moved by said fluid pressure, and other resilient means opposing the iiuid pressure acting on the plunger and contacted by said plunger to establish a second range of fluid pressures in the system.

11. A control system as described in claim 10, a pressure regulating valve connected to the output of one of the pumps and adapted to produce a maximum pressure which is less than the minimum required by the system, a conduit connecting one of the output ports to the said pump pressure regulating valve to admit fluid pressure to the pump pressure regulating valve in opposition to the pressure to be regulated to render the said pump pressure regulating valve ineffective to regulate pressure, and means for transferring the input of the pressure regulating valve from one pump to the other, said means being responsive to the difference in pressure produced by the two pumps, one of said outlet ports serving to vent the fluid pressure admitted to the pump pressure regulating valve to render the said pump pressure regulating valve effective, whereby the difference in pressure produced by the two pumps may favor the output member pump and cause said means to transfer the input to the pressure regulating valve to the said output member pump.

12. A control system as described in claim 10, and means for introducing fluid under pressure to the side of the plunger on which the resilient means acts to establish a third range of pressures in the system.

13. a pressure regulating valve comprising a valve body having a bore and a plurality of ports therein including an inlet port, a plunger in said bore, said. plunger having two peripheral grooves, one of said grooves in one position of the plunger being aligned with the inlet port and with an outlet port and the other of said grooves being aligned with a vent port andan inlet port, said plunger having cross bores connected to one groove and an axial bore connecting the cross bores with the end of the plunger such that fluid under pressure entering the groove will pass through the cross bores and axial bore to the end of the plunger to urge the plunger in one direction in the valve body bore, a tube secured to the end of the plunger opposite the end having the axial bore, a spring in the tube compressed between the tube and the valve body and opposing the fluid pressure, and a second spring in the bore disposed concentrically with respect to the first-mentioned spring and compressed between the end of the bore and an abutment in the bore, said plunger being adapted to exert pressure against the secl 1` ond spring after they first-mentioned spring lias been compressed a predetermined amount, whereby to provide tWo ranges of pressures in the output of the valve.

14. A pressure regulating Valve as described iny claim 13, and a sleeve interposed loetween` the plunger and said second spring to transmit the pressure of the plunger to said second'. spring, said sleeve. having a flange atone end and said valve body bore having an abutment contacted by the. flange to limit movement of the sleeve in the loore under the action of the said second spring.

Fil

UNITED STATES. PATENTS' Name Date Parker Oct. 29, 1940 Fieber et al. Sept. 9, 1941 Benham Feb. 24', 1948V Waldie Dec. 7', 1948 Trautrnan Apr. 19', 1949v Hollerith Sept. 20, 1949 

